1. Field of the Invention
The present invention relates generally to radio frequency (RF) transponders such as radio frequency identification (RFID) transponders, and more specifically, to an RFID transponder having a high gain antenna configuration.
2. Description of Related Art
In the automatic data identification and collection industry, the use of RFID transponders (also known as RFID tags) has grown in prominence as a way to track data regarding an object to which an RFID transponder is affixed. An RFID transponder generally includes a semiconductor memory in which information may be stored. An RFID interrogator containing a transmitter-receiver unit is used to query an RFID transponder that may be at a distance from the interrogator. The RFID transponder detects the interrogating signal and transmits a response signal containing encoded data back to the interrogator. RFID systems are used in applications such as inventory management, security access, personnel identification, factory automation, automotive toll debiting, and vehicle identification, to name just a few.
RFID systems provide certain advantages over conventional optical indicia recognition systems (e.g., bar code symbols). For example, the RFID transponders may have a memory capacity of several kilobytes or more, which is substantially greater than the maximum amount of data that may be contained in a bar code symbol. The RFID transponder memory may be re-written with new or additional data, which would not be possible with a printed bar code symbol. Moreover, RFID transponders may be readable at a distance without requiring a direct line-of-sight view by the interrogator, unlike bar code symbols that must be within a direct line-of-sight and which may be entirely unreadable if the symbol is obscured or damaged. An additional advantage of RFID systems is that several RFID transponders may be read by the interrogator at one time.
One important consideration in an RFID system is the range at which the radio frequency transponder may be read. A known method to increase the range of a radio frequency transponder is to increase the power of the interrogating signal, which necessitates a greater use of energy. A drawback of this method is that increasing the energy of the interrogating signal may involve adding additional and more costly components to an RF transmitter-receiver unit of the interrogator. This may prove costly not only to manufacture, but also to utilize in its intended environment. Another consideration in an RFID system is that, in some instances, it is desirable to selectively orient the field-of-view of an RFID transponder relative to an interrogating source, receiver, or the like. For example, the radio frequency transponder might be oriented so that it would respond to only one of two interrogating sources.
Consequently, it would be advantageous to provide an RF transponder with an increased effective range and/or a selective field-of-view in a cost effective and efficient manner.